1. Field of the Invention
The present invention relates to an air intake control system provided in an air intake line of an internal combustion engine.
2. Description of the Background Art
Generally, an air intake control system of an internal combustion engine employs an air intake control apparatus which includes an intake air control valve disposed in an inlet pipe connected to cylinders, the intake air control valve including a valve shaft and a valve element mounted pivotably about the valve shaft. The valve shaft is turned in a controlled fashion by an actuator, such as a motor, whereby the valve element is pivoted between a fully opened position and a completely closed position to adjust intake passage cross section of the inlet pipe.
For example, Japanese Patent Application Publication No. 2004-124933 discloses a variable air intake control apparatus including a valve element mounted on a valve shaft disposed in an intake passage within an intake manifold which is connected to engine cylinders. The valve element is mounted pivotably about the valve shaft which is supported by the intake manifold. A gear is fixedly mounted on the valve shaft and the valve element is controllably opened and closed by a driving force produced by a motor of which rotary shaft is fitted with a pinion that meshes with the gear of the valve shaft.
In the variable air intake control apparatus thus structured, the valve element goes into contact with a stopper at a fully opened position and at a completely closed position. One problem of this variable air intake control apparatus is that an impact load acts on the valve element due to inertia of the motor and of the gear fitted on the valve shaft when the valve element goes into contact with the stopper, causing an impact on meshing teeth of the gear fitted on the valve shaft and the pinion fitted on the motor shaft. Since contact areas of the meshing teeth carry the entirety of the impact load, the teeth of the gear and the pinion are likely to break.
One approach to reducing this impact load for overcoming the aforementioned problem is introduced in Japanese Patent Application Publication No. 1999-173116, which discloses an air intake control apparatus in which a gear (motor gear) fitted on a rotary shaft of a motor and a gear (throttle gear) fitted on a valve shaft carrying a valve element are helical gears, and the motor gear fitted on the rotary shaft is sandwiched by a pair of spring washers. The motor gear is mounted on the rotary shaft in such a manner that the motor gear can move along an axial direction of the rotary shaft but does not rotate relative to the rotary shaft. When the throttle gear goes into contact with a stopper and stops at a fully opened position or at a completely closed position, one of the spring washers is compressed and the other extends, whereby the motor gear moves along the axial direction of the rotary shaft and an impact load caused by inertia is alleviated.
The air intake control apparatus of Japanese Patent Application Publication No. 1999-173116 however poses the following problems:
(1) The helical gears are complicated in structure and are difficult to manufacture;
(2) The structure of the Publication, in which one of the helical gears sandwiched by the spring washers is mounted movably along the rotary shaft but unturnably around the rotary shaft, requires a larger number of components including the spring washers and stoppers therefor as well as a complex assembly process; and
(3) Foreign matter may intrude between sliding areas of the helical gear and the rotary shaft when the helical gear moves along the rotary shaft, or the spring washers may be damaged by repeated stress over the course of time, resulting in poor reliability of the air intake control apparatus.